X-ray image of the central region
of the starburst galaxy M82. Of particular
interest in this image is the bright source near the
center of the image, which is offset from the dynamical
center (small green +) of the galaxy by about 600 light
years. This source was seen to increase dramatically in
intensity over a period of three months (compare left
and right panels) after which it decreased in
intensity. A pattern of variability such as this
indicates that the source is a black hole.

This is the first confirmed case of such a large black
hole outside the nucleus of a galaxy, and is believed
to represent a new type of black hole formed by the
merger of scores of black holes, or by the collapse of
a "hyperstar" formed by the coalescence of many
stars.

Chandra observed M82 six times for approximately 30
hours total. Some of the observations were made with
the High Resolution Camera (HRC) and some with the
Advanced CCD Imaging Spectrometer (ACIS) X-ray camera.
The spread-out appearance of the X-ray source is an
instrumental artifact. The distribution of the X-rays
is consistent with this source being point-like.

Note: The previously announced 600-second oscillation
reported from M82 was found to be an artifact of the
data screening procedure used to eliminate spurious
events produced by the HRC detector electronics. This
does not alter the conclusion that confirmed the
existence of a mid-mass black hole 600 light years from
the center of the galaxy M82. That conclusion was based
on the observed intensity of the source and the
accurate location for the source, which are
unaffected.